There is an alternative approach available:
Unattended using timedatectl
First find out the name for the time zone you want to configure. The name is usually in the form <area>/<city> where area is a continent or ocean and city is a big city in that area (e.g. Europe/Berlin for Germany). timedatectl list-timezones will show the known time zones.
To update the time zone in Ubuntu 16.04 and newer non-interactively, call timedatectl set-timezone with the time zone and then reconfigure tzdata. Example for Europe/Berlin:
sudo timedatectl set-timezone Europe/Berlin
sudo dpkg-reconfigure -fnoninteractive tzdata
Explanation: timedatectl will update the /etc/localtime symlink and dpkg-reconfigure will set /etc/timezone.